International patent applications PCT/US2004/010851, filed Apr. 9, 2004 (published as WO2004/092166 on Oct. 28, 2004) and PCT/US2004/011280, filed Apr. 9, 2004 (published as WO2004/092168 on, Oct. 29, 2004), and U.S. application Ser. No. 10/838,835 (issued as U.S. Pat. No. 6,953,790 on Oct. 11, 2005) disclose compounds useful for the treatment of diseases or conditions of humans or other species which can be treated with inhibitors, modulators or promoters of the Calcitonin Gene-Related Peptide (CGRP) receptor function. Such diseases or conditions include those mentioned in the referenced applications, and specifically include migraine and cluster headache.    N-[(3R,6S)-6-(2,3-Difluorophenyl)-2-oxo-1-(2,2,2-trifluoroethyl)azepan-3-yl]-4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin-1-yl)piperidine-1-carboxamide, 1:
is a potent CGRP modulator. The laboratory preparation of compound 1 is described in international patent applications PCT/US2004/010851 and PCT/US2004/011280, and in U.S. patent application Ser. No. 10/838,835.
The laboratory preparation of certain intermediates employed in the synthesis of compound 1 is likewise described in the above-listed applications. Such intermediates include the intermediate (3R,6S)-3-amino-6-(2,3-difluorophenyl)-1-(2,2,2-trifluoroethyl)azepan-2-one, 2:
and the intermediate 2-oxo-1-(4-piperidinyl)-2,3-dihydro-1H-imidazo[4,5-b]pyridine, 3:
and salts thereof, including 2-oxo-1-(4-piperidinyl)-2,3-dihydro-1H-imidazo[4,5-b]pyridine dihydrochloride:
Prior techniques for synthesizing compound 1, including syntheses of intermediates 2 and 3, are relatively inefficient and costly from the standpoint of production and/or may result in sub-optimal salt and/or solvate forms for further synthesis and/or development.
With respect to intermediate 2, it has been found that prior techniques of synthesis require an inordinate number of steps, including a large number of isolation steps, making the overall synthetic process slow as well as costly. Thus there remains a need for an improved synthetic route to compound 1 wherein the synthetic route to compound 2 is efficient and economical.
Prior techniques for making intermediate 3 are likewise costly and inefficient. Such known routes start with a reductive alkylation of 2,3-diaminopyridine (“DAP”) followed by CDI-mediated cyclic urea formation and, lastly, acidic Boc-group deprotection/salt formation. This “DAP” route is characterized by high-cost starting materials and reagents as well as a low yielding first step, resulting in prohibitive overall costs. Thus, there remains a need for an improved synthetic route to compound 1 wherein the synthetic route to intermediate 3 is efficient and economical.
Finally, prior techniques for making compound 1, which techniques employ 4-nitrophenyl chloroformate as the carbonyl source, result in less than optimal yields. Such prior techniques further require that the neutral form of compound 1 be isolated prior to conversion to preferred salt forms. Moreover, previous laboratory-made forms of compound 1, including free base forms and salt forms, possessed less than ideal properties with respect to stability and bioavailability. Thus, there remains a need for an improved synthetic route to compound 1, and pharmaceutically acceptable salts thereof, which is amenable to large scale production formulation, storage and distribution.